1. Field of the Invention
The present invention relates to selective and thermally reversible adsorption of NO.sub.x from a mixture of hot gases by surface actions with copper in the form of CuO on a support material, such as TiO.sub.2 and SiO.sub.2, and in the form of Cu.sup.+2 on pillared clays. The selective and thermally reversible NO.sub.x adsorption is particularly useful for treatment of internal combustion engine and power plant effluents.
2 Description of Related Art
Selective catalytic removal of NO.sub.x has been a most effective means for NO.sub.x abatement. V.sub.2 O.sub.5 /TiO.sub.2 has been the principal commercial catalyst used for selective catalytic removal with NH.sub.3 from stationary sources. Bosch, H; Janssen, F., Catal. Today, 1988, 2, 369. Noble metals Pt--Rh--Pd catalyst is the catalyst used in automobiles, primarily for removal of CO. Taylor, K. C., Catal. Rev. Sci. Eng., 1993, 35, 457, and Zwinkels, M. M.; Jarus, S. G.; Menon, P. G., Catal. Rev. Sci. Eng., 1993, 35, 319. The noble metal catalyst is effective as a three way catalyst, however, it suffers severe loss of activity for NO reduction in the presence of excess oxygen prevalent in exhaust from diesel and lean-burn engines. Other tri-metal three way catalysts are described in U.S. Pat. Nos. 5,108,716; 5,386,690; 5,593,647 and 5,322,671. Other catalysts which have attracted interest as hydrocarbon selective catalytic removal catalysts are Cu--ZSM-5, Iwamoto, M.; Mizuno, N., Proc. Inst. Mech. Eng., Part D, 1993, 207, 23 and Held, W.; Konig, A.; Richter, T.; Puppe, L., SAE Tech. Pap., 1990, No. 900, 469, and Co--ZSM-5, Li, Y.; Battavio, P. J.; Armor, J. N., J. Catal., 1993, 142, 561. However, these catalysts are deactivated rapidly by moisture and SO.sub.2. Li, Y.; Battavio, P. J.; Armor, J. N., J. Catal., supra; Armor, J. N., Appl. Catal. B., 1995, 5, N18 and Li, Y.,; Armor, J. N., Appl. Catal. B, 1995, 5, L257. A most promising selective catalytic reduction catalyst for reduction of NO by hydrocarbons and by ammonia has been Cu.sup.2+ exchanged TiO.sub.2 -pillared clays exhibiting high activities and low deactivation by H.sub.2 O and SO.sub.2. Yang, R. T.; Li, W. B., J. Catal., 1995, 155, 414. Selective catalytic reduction of nitric oxide by ethylene over Cu.sup.2+ ion-exchanged pillared clays is taught by Li, W. B.; Sirilumpen, M.; Yang, R. T., Appl. Catal., 1997, 11, 347.
Ceria is known to be an effective promoter for the NO selective catalytic removal reaction with NH.sub.3, Chen, J. P.; Hausladen, M. C.; Yang, R. T., J. Catal., 1995, 151, 135, and with hydrocarbon, Yang, R. T.; Li, W. B., J. Catal., 1995, 155, 414. Ceria alone, however, does not chemisorb NO at elevated temperatures. Niwa, M.; Furukawa, Y.; Murakami, Y., J. Colloid. Interface Sci., 1982, 86, 260.
Staged, or series arranged, catalytic converters for purifying exhaust gases from internal combustion engines are described in U.S. Pat. Nos. 5,512,251; 5,399,324 and 5,556,604.
U.S. Pat. No. 5,388,406 teaches purification of exhaust of an internal combustion engine using as an absorbent a composite oxide of copper and an alkali metal, alkali earth, and/or rare earth, which may be cerium coated, for absorption and thermal release of NO.sub.x followed by catalytic NO.sub.x decomposition. This patent teaches that NO cannot be absorbed by the NO.sub.x absorption/release material. This patent is based upon absorption of NO.sub.x to form Ba(NO.sub.3).sub.2, or alkali nitrate, where CuO functioned as a catalyst. The process of this patent does not use the adsorption ability of CuO. Another method, applicable to lean-burn engines, is to dope noble metals on the sorbent and to operate the engine with pulses of rich-burn conditions, during which time adsorbed NO.sub.x decomposes to N.sub.2. Brogan, M. S.; Brisley, R. J.; Walker, A. P.; Webster, D. E.; Bogner, W.; Fekete, N. P.; Kramer, M.; Krutzsch, B.; Voigtlander, D., SAE Tech. Pap., 1995, No. 952, 490 and Bogner, W.; Kramer, M.; Krutzsch, B.; Pischinger, S.; Voigtlander, D.; Wenninger, G.; Wirbeleit, F.; Brogan, M. S.; Brisley, R. J.; Webster, D. E., Appl. Catal. B, 1995, 7, 153.
A promising alternative for hydrocarbon selective catalytic removal is NO.sub.x trapping, or adsorption/absorption of NO.sub.x at high temperatures with a very NO.sub.x specific sorbent. Such a sorbent must be able to selectively adsorb NO.sub.x from oxygen-rich combustion gases which also contain H.sub.2 O, SO.sub.2, CO.sub.2 and N.sub.2 at temperatures of about 150.degree. to about 350.degree. C., depending upon the specific application. The sorption rates must be high, for example, suitable for applications at space velocities of greater than about 3000 l/h. The sorption must be reversible either by increasing temperature or decreasing pressure, so that a desorption stream concentrated in NO.sub.x can be obtained. Yang, R. T., Gas Separation by Adsorption Processes, Butterworth, Boston, 1987, Chapter 5. The concentrated stream can be recycled to a combustion zone for decomposition of NO to N.sub.2. Desorption/decomposition can also be achieved by injection of a reducing gas. The searches for an advantageous sorbent for NO.sub.x have been reviewed by Kaneko, K.; Inouye, K., Adsorpt. Sci. Technol., 1988, 5, 239 and Arai, H.; Machida, M., Catal. Today, 1994, 22, 97. Transition metal oxides sorbents have been described by Otto, R.; Shelef, M., J. Catal., 1970, 18, 184, Yao, H. C.; Shelef, M., In The Catalytic Chemistry of Nitrogen Oxides, Klimisch, R. L.; Larson, J. G.; Eds., Plenum, New York, 1978, 45, Segawa, K.; Chen, Y.; Kubsh, J. E.; Delgass, W. N.; Dumesic, J. A.; Hall, W. K., J. Catal., 1982, 76, 112, Yuen, S.; Chen, Y.; Kubsh, J. E.; Dumesic, J. A.; Topsoe, N.; Topsoe, H., J. Phys. Chem., 1982, 86, 3022, Lund, C. R. F.; Schorfheide, J. J.; Dumesic, J. A., J. Catal., 1979, 57, 105. Sorbents of ZSM-5 or MFI zeolites exchanged by Cu.sup.2+ and other cations have been described by Zhang, W.; Yahiro, H.; Mizuno, N.; Izumi, J.; Iwamoto, M., Langmuir, 1993, 9, 2337. Sorbents of Fe.sub.2 O.sub.3 dispersed on activated carbon fibers have been described by Kaneko, K., Langmuir, 1987, 3, 357 and Kaneko, K., Colloid Surf., 1989, 37, 879. Zeolites as sorbents have been described by Joithe, W.; Bell, A. T.; Lynn, S., Ind. Eng. Chem. Process Res. Dev., 1972, 11, 434 and Zhang, W. X.; Yahiro, H.; Mizuno, N.; Izumi, J.; Iwamoto, M., J. Mater. Sci. Lett., 1993, 12, 1197. Y--Ba--Cu--O as sorbents have been described by Tabata, K.; Fukuda, H.; Kohiki, S,; Misono, M., M. Chem. Lett. 1988, 799 and Mizuno, N.; Yamato, M.; Misono, M., J. Chem. Soc., Chem. Commmun., 1988, 887. Carbon as an adsorbent has been described by Rubel, A. M.; Stencil, J. M., Energy Fuels, 1996, 10, 794. Mixed metal oxides as sorbents have been described by Brogan, M. S.; Brisley, R. J.; Walker, A. P.; Webster, D. E.; Bogner, W.; Fekete, N. P.; Kramer, M.; Krutzsch, B.; Voigtlander, D., supra, Bogner, W.; Kramer, M.; Krutzsch, B.; Pischinger, S.; Voigtlander, D.; Wenninger, G.; Wirbeleit, F.; Brogan, M. S.; Brisley, R. J.; Webster, D. E., supra, and Machida, M.; Yasuoko, K.; Eguchi, K.; Arai, H. J., J. Chem. Soc., Chem. Commun., 1990, 1165. Mixed metal oxides of Mn--Zr (1:1 molar ratio) having most promising NO.sub.x capacity and rate of uptake of prior sorbents have been reported by Eguchi, K.; Watabe, M.; Ogata, S.; Arai, H., J. Catal., 1996, 158, 420.
CuO supported on .gamma.-Al.sub.2 O.sub.3 has been studied for NO.sub.x adsorption at room temperature by Yao, H. C. and Shelef, M., supra. However, sulfation of .gamma.-Al.sub.2 O.sub.3 takes place at elevated temperatures resulting in pore closure due to increase in the crystalline volume. Num, I. S.; Eldridge, J. W.; Kittrell, J. R., J. R. Ind. Chem. Prod. Res. Dev., 1986, 25, 192, Nam, S. W.; Gavalas, G. R., Appl. Catal., 1989, 55, 193 and Yoo, K. S.; Kim, S. D.; Park, S. B., Ind. Eng. Chem. Res., 1994, 33, 1786. It has been reported that NO at 1000 ppm does not chemisorb on V.sub.2 O.sub.5 on a TiO.sub.2 support at temperatures above 300.degree. C., but does chemisorb at temperatures as high as 400.degree. C. on sulfated TiO.sub.2 surface, formed by exposure of TiO.sub.2 to SO.sub.2 and O.sub.2 at low concentrations. Chen, J. P.; Yang, R. T., J. Catal., 1993, 139, 277.
Portions of the present invention are described in Li, W. B.; Yang, R. T.; Krist, K.; and Regalbuto, J. R., Energy & Fuels, 1997, 11, 428, which is incorporated herein in its entirety by reference.